In recent years, development in robots is remarkable such that robots performing a variety of motions are appearing. Further, a wearable electronic device capable of being attached to a human body or clothing is also being developed and put to practical use in various devices. Although, in these robots and wearable electronic devices, a large number of electric wires for power supply and for transmission of electrical signals are used, in general, an electric wire is structured such that a copper wire is used as a core, and an outer periphery of the copper wire is covered by an insulator, so that the electric wire itself does not have extension/contraction property almost at all. For this reason, in a robot or the like, there is a need to provide a margin to a length of electric wire so as not to prevent a motion and the like of a joint of the robot or the like, which becomes an obstacle in terms of design and practical use for downsizing, reduction in weight and the like.
Particularly, when a front-line humanoid-type robot, a power assist device which is attached to a human body to assist muscular power, or the like is used, a large number of electric wires for moving a terminal motor via multiple-degree-of-freedom joints and a large number of electric wires for transmitting electrical signals from various types of sensors disposed at terminal end are wired. Further, in order to increase a degree of freedom of these wires in the multiple-degree-of-freedom joints, a demand with respect to electric wires configured in an extendable/contractable manner is increasing.
Meanwhile, arm robots are often used as industrial robots in recent years. In this type of arm robots, depending on a drive system of an end effector (which is equivalent to a hand in a human body) attached to a tip side of the robot arm and a joint part of the robot arm, there is sometimes generated a necessity to arrange, other than electric cables, an air hose for application of pneumatic pressure or a hydraulic hose from a root side to the tip side of the robot arm. When such cables and hoses are arranged in a joint part, there is a chance that bending or disconnection of the cables occurs. Accordingly, there is adopted a wiring method such that the cables and the hoses are once taken out to the outside at a position on a base end side relative to a joint part of the robot arms, the cables are arranged in an outside space of the joint part, and then introduced again into the arm at a position on a tip side relative to the joint part. However, in the method of arranging the cables in the outside space of the robot arm, it becomes required to provide the space for slackening the cables to the periphery of the joint part of the robot arm.
Further, PTL1, for example, discloses a structure in which a support rod is provided at a rotation center position of joint in a joint part of a robot arm, a cable is wound around the support rod, and the support rod around which the cable is previously wound is housed in the inside of the robot arm, thereby preventing bending or disconnection of the cable. However, there is a chance of causing a reduction in functions (operating speed, accuracy and the like) due to an increase in weight caused by separately providing the support rod. There is sometimes a case where a motor or the like with high specification is used or a number of required members is increased for compensating the reduction in functions, but, in that case, a manufacturing cost is increased. Besides, a structure of a housing part of the cable becomes complicated, so that there is a problem that a work when performing wiring of the cable during an assembly of the robot arm, and when performing disassembly in the case of maintenance or the like, in which the cable is taken out and exchanged, becomes complicated very much. From this point, also in the robot arm, a demand with respect to an extendable/contractable electrical transmission member which can avoid such a problem, is increasing.
As a technique which responds to such a requirement with respect to the electrical transmission member, there is one disclosed in PTL2, for example. Such PTL2 describes a method in which a plurality of pieces of pins each formed to have a desired R are arranged in a jig at an interval at which a flexible printed circuit board can be passed, and heat-molding is performed by passing the flexible printed circuit board while applying a constant tension to the jig.
Further, regarding the structure of the flexible printed circuit board, PTL2 discloses not only a single-sided flexible printed circuit board having a conductive layer only on its one side, but also a three-layer flexible printed circuit board having conductive layers formed of three layers. The three-layer flexible printed circuit board is generally used for a so-called strip line transmission path in which a signal line having matched characteristic impedance is arranged on an inner layer, and an outer layer is set as GND (ground). The three-layer flexible printed circuit board is required when, for example, an image sensor is attached to a tip side of the aforementioned movable part, and large-capacity data such as high-definition moving image data is transmitted via an extendable/contractable flexible printed circuit board, in which it is aimed to block a noise from the outside and to realize both of high-quality signal transmission and extension/contraction property.
Further, PTL3 discloses a configuration in which a ground of an outer layer of a flexible printed circuit board is not set to a solid GND in a solid state but is set to have a mesh structure, to thereby reduce a generation of stress concentration with respect to a bent portion.